Subsea production system

ABSTRACT

A subsea production method and apparatus separates substantially waterfree gas from oil in a subsea satellite located adjacent a plurality of subaqueous wells. Production fluid from the subaqueous well enters the satellite through production fluid lines, passes through a heat exchanger, and enters into a liquid knockout section. Separated gas and oil then enter into a lowtemperature separator to complete the separation of the substantially waterfree gas from the oil. A hydrate depressant is injected into the substantially waterfree gas before entry into the low-temperature separator through a variable choke so as to depress the formation of hydrates from any water remaining in the substantially waterfree gas.

I United States Patent H 13,590,919

[72] Inventor WilliamA.Talley,Jr. 3,469,627 9/1969 Baker 166/.5 Dallasfl'ex. 3,495,380 2/1970 Remanetal 166/.5 1 1 Apr 855'961 OTHERREFERENCES 23 ir 'z gf Submerged Capsule Challenges Offshore Operating [73] Assignce Mobnoncorporafiou Problems" WORLD OIL, October 1968, pages 122-- 124,

[54] SUBSEA PRODUCTION SYSTEM 5 Claims, 4 Drawing Figs.

52 U.S.Cl 511 meet. so FieldofSearch Primary Examiner-James A. Leppink Attorneys-William J. Scherbaek, Frederick E. Dumoulin,

Drude Fauleoner, Andrew L. Gaboriault and Sidney A. Johnson ABSTRACT: A subsea production method and apparatus separates substantially waterfree gas from oil in a subsea satellite located adjacent a plurality of subaqueous wells. Production fluid from the subaqueous well enters the satellite through production fluid lines, passes through a heat exchanger, and enters into a liquid knockout section. Separated gas and oil then enter into a low-temperature separator to complete the separation of the substantially waterfree gas from the oil. A hydrate depressant is injected into the substantially waterfree gas before entry into the low-temperature separator through a variable choke so as to depress the formation of hydrates from any water remaining in the substantially waterfree gas.

PATENTEUJUL 6l97| 3.590.919

sum u 0F 4 SUBSEA PRODUCTION SYSTEM BACKGROUND OF TH E INVENTION This invention relates to a subsea production satellite system for use with subaqueous wells, and more particularly, to a subsea production satellite system for use with gasproducing subaqueous wells.

Presently available statistics indicate that the reserve-to production oil ratio is diminishing and thereby indicating the need to tap heretofore untapped reserves. In response to this need, the offshore oil and gas industry has located and produced from various offshore fluid mineral deposits. lni tially, production was limited to the coast waters of California and the Gulfof Mexico because of the shallow nature of these waters and consequent ease in producing from the mineral deposits located in these areas. However, as the reserves in these areas began to diminish, there was a need to extend production into various deepwater areas.

While various systems have now been developed which permit deepwater oil production, and in particular the subsea oil production satellite systems as disclosed in US. Pat. No. 3,401,746 and US. Pat. No. 3,366,l73, assigned to the assignee of the present invention, the subsea oil production system may not be successfully utilized in subsea gas production. Although the same conditions which dictated the use of subsea satellites in oil production would appear to dictate the use of a similar subsea satellite for use in gas production; i.e., the economical and technological infeasibility of a bottomsupported permanent surface installation, the extremely cold temperatures of the subsea bottom in these deepwater areas will not permit the use of the presently available production apparatus utilized in the subsea oil production satellites for the following reasons.

At the present time, the only economically and technologically feasible method of transporting or shipping gas is a pipeline. However, in shipping gas through a submerged pipeline in a deepwater area, the gas will be subjected to temperatures of the order of 35 F. which are sufficiently cold to cause hydrate formation within the pipe. The effect of the hydrate formation is to clog the pipeline. In the subsea production satellites used in producing oil from predominantly oil-bearing formations, there has been failure to obtain a substantially waterfree gas which could then be sold as a product in itself. In certain subsea oil production satellites, the gas is utilized as an aid in shipping the oil liquid product and the gas itself is not utilized as a product and therefore there is no need to obtain a substantially waterfree gas. In other subsea oil production satellites, the substantially wet gas is separated from the oil of the production fluid so that the gas may be utilized for pressure maintenance and well production increase.

Furthermore, even if hydrate formation could be sufficiently retarded, the gas pipeline would not be feasible for long distances if the gas were at all wet. The reason for this lies in the fact that tremendous friction losses are inherent in the use of a pipeline for a liquid product so as to necessitate the use of prohibitively expensive compressor stations en route to the user market along the pipeline to overcome these friction losses. Thus it is not feasible to ship a wet gas over a long pipeline utilizing submerged compressor stations nor is it feasible to utilize a pipeline to ship combined oil and gas over long distances through a submerged pipeline having submerged compressor stations associated therewith. It is for this reason that oil as a liquid product is shipped over long distances by tankers which are filled with oil from a riser extending from the subsea satellites to the surface thereby avoiding the necessity for a long-submerged pipeline.

It will therefore be appreciated that the art as it presently stands will not permit production of a gas product from offshore deepwater fluid mineral deposits. As a consequence, the gas reserves of certain known oil-producing subaqueous deepwater wells are not used. Furthermore, certain fluid mineral deposits which are capable of producing primarily gas or having a high GOR (gas to oil ratio) remain completely untapped. In some instances, these primarily gas deposits are relatively close to shores having a very dense user market thereby suggesting that gas pipelines could be utilized to ship a gas product to this dense user market at a minimum of pipeline cost if a sufficiently waterfree gas could be obtained. However, the subsea satellite production systems for use in deep water as they presently exist do not have the capability of producing a sufficiently waterfree gas to permit the development of these rather close offshore deepwater deposits.

SUMMARY OF THE INVENTION It is therefore an object of this invention to provide a means and method for producing gas from heretofore untouched subaqueous gas deposits.

It is also an object of this invention to provide a means and method for producing gas from deep existing subaqueous oilproducing wells.

It is a further object of this invention to provide a means and method for producing a substantially waterfree gas.

It is a still further object of this invention to provide a means and method for producing a substantially hydratefree gas.

In accordance with these objects, the means and method provided achieve a separation ofa substantially waterfree gas from the liquid of the production fluid obtained from a deepwater, gas-bearing, subaqueous well.

The means and method may comprise a subsea satellite production system including heat exchange means for condensing substantially all fluid in the production fluid except for the gas, a knockout section to achieve the initial separation of the gas from various other production fluids including oil or water, and a low-temperature separator means for completing 1 the separation of oil and gas prior to shipping of substantially waterfree gas through a gas product line. In order to prevent the formation of hydrates from any water remaining in the substantially waterfree gas, a hydrate depressant may be injected into the gas.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a perspective view of a deepwater gas production system including subsea satellites;

FIG. 2 is a flow diagram of production apparatus enclosed DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring first to FIG. I for disclosure of an overall subsea production system 10, there will be seen a plurality of subsea production satellites 12 located as a group at a subaqueous bottom 14. All of the satellites 12 have product lines 16 extending outwardly therefrom to a generally centrally disposed riser base and manifold 18 which serves as a central station for disbursement of gas and any liquid products produced by the satellites I2.

In order to achieve the disbursement of the gas-and any liquid products, a gas-shipping line 20 extends outwardly away from the riser base and manifold 18 and along the subaqueous bottom 14 to shore and direct consumption by usersJAny liquid products are disbursed by use of a riser 22 which extends upwardly from the riser base and manifold 18 to a suitable floating facility capable of storing oil or any other product condensate produced by the satellite I2.

For illustrative purposes, the floating facility 24 has been shown as a storage tanker and the satellites 12 have been shown as having a earrousel configuration similar to that disclosed in U.S. Pat. application Ser. No. 740,578, filed June 27,

I968 assigned to the assignee of this invention. It is however appreciated that the facility 24 might be replaced by a shallower water platform, a centrally located platform for pumping water to shore, or another floating or shore storage facility.

It is also appreciated that the satellites 12 need not be of the carrousel type operating in conjunction with a plurality of radially outwardly spaced subaqueous wells having submerged wellheads but rather might be a subsea satellite of a completely different configuration and operating in conjunction with a single well having a submerged wellhead. In other words, the essence of this invention is not the outward appearance of the storage facility 24 or satellites 12 but rather the production capability of the satellites I2 which permit substantially waterfree and hydratefree gas to be shipped through the shipping line 20.

Reference is now made to FIG. 2 in order to explain the method and apparatus of obtaining substantially waterfree and hydratefree gas from each satellite 12. As hot production fluid enters the satellite 12 through a production line 26, the hot production fluid coming directly from a subaqueous well passes through a manual control valve 28 and an automatically actuated fail-safe valve 30 connected in series therewith. The manual valve 28 may be closed by personnel entering the satellite 12 when performing a servicing function and the failsafe valve 30 is closed in response to emergency conditions such as excessive temperature or pressure within the satellite 12.

The hot production fluids are next passed through to a lowtemperature separator unit 32 while still enclosed within the production line 26 in order to provide a heat exchange function. The heat exchange function is necessary in order to cool the hot production fluid and thereby condense the maximum amount of water vapor and liquid products out of the gas in the production fluid if substantially waterfree gas is to be obtained and the gas is to be separated from the liquid products. Accordingly, the production line 26 extends through an upper gas portion 34 and down into a lower oil portion 36 so as to accomplish a more thorough heat exchange. The somewhat cool production fluid then passes out of the low-temperature separator while still in the production line 26. It will be noted that there is no fluid communication between the production fluids within the production line 26 and the fluids within the low-temperature separator 32. Rather, there is only heat communication through the walls of the production line 26 so as to provide the heat exchange function within the low-temperature separator 32.

After the heat exchanger function is accomplished within low-temperature separator 32 the production fluid passes from the low-temperature separator 32 through the produc tion line 26 to a phase knockout section 38. If it is desirable to separate 'water from oil as well as gas from oil and water, a three-phase knockout section is utilized. A water line 40 is connected to the lower portion of the knockout section 38 to provide means for draining water therefrom to the surrounding sea, a storage tank internal to the satellite 12, or a connection 42 to a liquid product line 44. Oil is drained from the lower portion of the knockout section 38 through an oil line 46 into the lower oil portion 36 of the low-temperature 32.

Gas separated within the liquid knockout section 38 is passed to the gas section 34 of the low-temperature separator 32 through a variable choke 48 in the gas line 50. The primary function of the choke 48 is to limit the flow of gas from the subaqueous wells to a gas product line 52 connected to the gas section 34 of the low-temperature separator 32. The secondary function of the choke 48 is to cause a sudden expansion of the gas as it passes through a restricted orifice at the choke 48 thereby permitting additional condensation of fluids in the gas so as to assure a more waterfree gas for the gas product line 52.

Theoretically, thegas entering the product line 52 will be substantially waterfree thereby preventing hydrate formation therein. For purposes of this specification, substantially waterfree is defined as free of water in liquid form. However, as a practical matter, it is virtually impossible to separate all of the water out of the substantially waterfree gas which enters the product line 52 so that hydrate formation will occur therein unless an effort is made to depress that formation. In this connection a hydrate depressant may be injected into the gas line 50 before the gas reaches the choke 48 in the form of glycol, or some other hydrate depressant such as methonal. The injection of the hydrate depressant may be accomplished through a depressant line 54 connected into the gas line 50 between the choke 48 and the knockout section 38. The other end of the glycol line 54 may be coupled to a glycol supply 56, a glycol pump 58 pumping the glycol within the glycol supply 56, and a glycol-metering device 60 for controlling the amounts of glycol to be injected through the line 54 as required to prevent hydrate formation of the gas within the gas product line 52.

By utilizing the low-temperature separator 32 as a heat exchange means, and more particularly by passing hot production fluid through the production line 26 within the interior of the low-temperature separator 32, the walls of the low-temperature separator 32 will be maintained at a sufficiently high temperature to prevent the formation of paraffin on the walls of the oil section 36. It is appreciated that paraffin formation can be an extremely critical problem in a subsea satellite wherein the external temperature is approximately 35 F. Thus the utilization of the low-temperature separator as a heat exchange means is particularly important in production with a subsea satellite. Of course, paraffin formation on the liquid product line 44 may be handled by a conventional pig launcher 62 coupled to the line 44 adjacent the low-temperature separator 32.

In certain instances, the overall heat exchange provided by the apparatus and method disclosed in FIG. 2 will not be sufficient to condense the liquids out of thegas so as to obtain a substantially waterfree gas. In those instances, it is necessary to provide a better heat exchange means and such a means will now be discussed with reference to FIG. 3.

The method and means disclosed in FIG. 3 are similar to the method and means disclosed in FIG. 2 and, for this reason, elements common to FIG. 2 and FIG. 3 carry identical numbers. The difference in the method and means of FIG. 3 is the addition of a secondary heat exchanger means 64 and means associated therewith in order to supplement the heat exchange provided by the primary heat exchanger in the form of the low-temperature separator 32. Thus, as the hot production fluid enters the satellite through the production line 26, it may be carried through the primary heat exchanger in the form of the low-temperature separator 32 and on through the secondary heat exchanger 64.

Even when the secondary heat exchanger 64 is present, the heat exchange capability thereof may not be utilized if the low-temperature separator 32 provides sufficient heat exchange to cool the hot production fluid. In such a situation, the substantially waterfree gas which is relatively cold as compared with the hot production fluid entering the production line 26 is routed directly to the gas product line 52 through a gas outlet line 66 leading from the gas section 34 of the lowtemperature separator 32 and a gas product shunt line 68 as long as a flow volume control valve 70 in the gas product shunt line 68 is open. When the temperature of the gas leaving the knockout section 38 and passing through the choke 48 in the gas line 50 reaches a predetermined elevated level, a temperature-sensing element 72 will actuate and close the valve 70 to divert the relatively cold gas through a heat exchange line 74 which extends through the additional heat exchanger 64 to the gas product line 52. When the valve 70 is closed, substantial heat exchange occurs between the relatively warm production fluid passing through the additional heat exchanger 64 and the relatively cold, substantially waterfree, gas also passing through the heat exchanger 64 to effect a more complete condensation of the liquids out of the production fluid.

Having now described the method of separating substantially waterfree and hydratefree gas from production liquids and having generally referred to the apparatus utilized in performing this method, the specific apparatus utilized will now be described in somewhat fuller detail with reference to FIG.

4. As shown, the production line 26 extends into a watertight, pressure-resistant shell 76 enclosing the satellite and on into the low-temperature separator 32. The manual valve 28 and the fail-safe valve 30 are located on the production line 26 internally of the shell 76 and externally of the low-temperature separator unit 32. As indicated, the manual valve 28 is substantially conventional as is the fail-safe valve 30 which is automatically actuated by a hydraulic control line 78 which is shown as abbreviated in order to simplify the drawing but is in actuality connected to a hydraulic system including a hydrau lic pump 80. As described previously, fail-safe valve 30 is sensitive to extreme pressure, temperature, or any other variables which might indicate an emergency situation within the satel lite as in the case of a leak in the shell 76 or the various lines enclosed within.

The production line 26 is shown as extending through the wall of the low-temperature separator 32 above a gas-oil level 82 with a substantial portion of the production line 26 extending below the gas-oil level 82 so that a substantial portion of the heat exchange function is provided by the oil section 36. Consequently, paraffin will be maintained in a liquid state due to the elevated temperatures provided by the hot production fluid passing through the oil section 36 and thereby limit the plating out of paraffin on the walls of the low-temperature separator 32 in the oil section 36. Although FIG. 4 has been simplified by showing the production line 26 as having a substantially U-shaped path through the oil section 36, it may be desirable to provide the helical path indicated in FIGS. 2 and 3 to permit more effective heat exchange between the hot production fluid and the oil of the oil section 36.

After extending through the wall of the low-temperature separator, the production line 26 extends through the wall of the knockout section 38 to permit the somewhat cool production fluid to begin the knockout step in the separation process. An end 86 of the production line is located in the middle of the knockout section 38 to permit liquids to drop under the force of gravity to the bottom while gas may rise to the top of the liquid knockout section 38. In this particular embodiment where it is desirable to separate gas from the liquids as well as separate liquids into gas and oil, a three-phase knockout section is utilized having an oil compartment 88 and a water compartment 90 located at the lower leftand right-hand sides of the bottom of the knockout section 38 respectively. The oil compartment 88 and the water compartment 90 are separated by a partition 92. As the production fluid passes from the end 86 and falls under the force of gravity toward the bottom of the knockout section 38, all liquid of the production fluid is initially forced into the water compartment 90 since the oil com partment 88 is covered by a bracket-mounted splash guard 94. Because the oil is substantially lighter than the water of the production liquid, the oil will collect within the water compartment 90 above an oil-water line 96 while the water collects below the line. A space is provided between the top of the partition 92 and the splash guard 94 to permit oil to flow over the top of the partition 92 and into the oil section 88 when the overall liquid level of the water compartment 90 exceeds the height of the partition 92.

In order to control the removal of the liquids from the oil compartment 88 and the water compartment 90, the oil and water lines 46 and 40 are located in the oil compartment 88 and the water compartment 90 respectively having dump valves 102 and 104 associated therewith.

The dump valve 102 for the oil line 46 is pneumatically operated by a float control means 105 having a float element 106 riding the surface 108 of the oil. The gas for the pneumatic actuation of the dump valve 102 is obtained from the gas available in the upper portion of the knockout section 38 and applied to the dump valve 102 through a supply line 110 passing through the valve control means 105 and down to the valve 102 through a control line 112. The gas may then be returned to the gas section 34 of the low-temperature separator 32 through a return line 114.

The dump valve 104 of the water line 40 is similarly achieved by utilizing a float actuated control element 116 to pneumatically actuate dump valve 104 through a pneumatic supply line 117, a control line 118, and the return line 114. However, a float element 120 of the control 116 must sense the oil-water level 96. Accordingly the float element 120 is of the differential type to permit the float to ride the interface of the oil and water. With the dump valves 102 and 104 properly controlled by the foregoing control means, oil from the oil compartment 88 will flow through the oil line 46 and into the oil section 36 of the low-temperature separator 32, and water from the water compartment 90 is dumped overboard through the water line 40. In order to prevent oil from surging into the oil section 36 of the low-temperature separator 32, a choke 122 is provided in the oil line 46.

Having now separated a substantial volume of liquid from the gas of the production fluid, the gas may be removed from the knockout section 38 by a mist extractor 124. The mist extractor 124, which has a lower tilted edge 126 to permit the condensate to drain free, is coupled to the gas section 34 of the low-temperature separator 32 through the gas line 50. Before reaching the gas section 34, the gas will flow through a variable choke 130 which may be controlled from a suitable control facility such as the storage facility 24 so as to permit control of the gas production from the subaqueous well associated therewith. A flow-measuring element 132 is provided in the gas line 50 head of the choke 130 to provide an indication to that control facility as to the flow of gas from the particular subaqueous well associated therewith.

Although the gas flowing from the gas line 50 into the gas section 34 will be substantially waterfree and particularly so after the condensation of liquids in the gas upon sudden expansion of the gas after passing through the choke, hydrate formation is still possible in the gas product line 52. Accordingly, in addition to making the gas substantially waterfree, it may be desirable and many times necessary to depress the formation of hydrates by injecting a hydrate depressant into the gas line 50. This may be accomplished by connecting the glycol line 54 to the gas line 50 and to the glycol-metering device 60 attached to the shell 76 of the satellite. By utilizing a timing element 134 in conjunction with the glycol-metering device 60, precisely metered amounts can be periodically injected into the gas line 50 as required by the specific amount of flow through the variable choke 130 as sensed by the flowsensing element 132. The timing element 134 also permits the use of the single glycol-metering metering device 60 to supply other gas lines leading into the low-temperature separator 32 which derive the gas flowing thereto from other subaqueous wells. The glycol to be injected into the gas line 50 as well as other gas lines is stored within the glycol supply reservoir 56 located at the lower portion of the satellite and pumped therefrom through a filter 136 and a glycol supply line 138 by the glycol pump 58 operating in conjunction with a motor 140. Both the pump 58 and the motor 140 are mounted on a bracket 142 extending from the shell 76 of the satellite.

The removal of the gas entering the gas section 34 of the low-temperature separator 32 is accomplished through a mist extractor 144 enclosed within the low-temperature separator unit and connected to the gas product line 52. The oil entering the low-temperature separator 32 is removed by the liquid product line, in this embodiment, the oil product line 44 which extends from the lowermost portion of the oil section 36. The draining of oil from the oil section 36 through the oil product line 44 is controlled by a float-actuated dump valve 146. The valve 146 is actuated by a float control mechanism 148 including a float element 150 which is located at the surface of the oil and pneumatically actuates the dump valve 146 through a control line 152. A pneumatic return line 154 is also provided between the dump valve 146-and the gas section 34.

As mentioned previously, the sudden expansion of the gas flowing through the choke 130 will result in some condensation of liquids out of the gas as it enters the low-temperature separator. For this reason, a splash guard 156 is provided adjacent to the float element 150 to prevent any condensate from improperly actuating the dump valve 146. Inthe event the dump valve 146 fails to keep the oil level sufficiently low within the low-temperature separator unit 32 so as to run the risk of oil entering the gas line 50 or the gas product line 52, a high-level-oil-sensing element is provided beneath the gas line 50 and in communication with the interior of the low-tem perature separator unit 32. When the oil level reaches the high-level-sensing element 158, the operation of the entire satellite will be shut down. Similarly, a low-level-sensing element 160 is also provided to prevent the oil level from becoming sufficiently low to allow gas to pass through the oil line 46 or the oil product line 44. The sensing element 160 is therefore positioned just above the connection of the oil line 40 into the oil section 36 of the low-temperature separator 32.

immediately beneath the low-temperature separator unit 32, there is a drain 162 which permits water condensing on the exterior of the relatively cold low-temperature separator 32 and other cold surfaces to be removed from the upper regions of the satellite. The drain 162 communicates with a sump 164 located immediately above the glycol supply reservoir 56. A hydraulic reservoir 166 is located immediately above the sump 164 to provide a source of hydraulic fluid to the pump 80. When the pump 80 is driven by a motor 172, hydraulic fluid is brought up from the reservoir 1166 through a filter I68 and a hydraulic fluid supply line 170. A hydraulic level indicator 174 may be utilized to provide the control facility with information as to the necessity to replenish the hydraulic fluid in the reservoir 166.

The apparatus utilized in carrying out the embodiment of FIG. 3 would be essentially identical to that disclosed in FIG. 4 except for the addition of the secondary heat exchanger 64 which might be located above the low-temperature separator 32 and the various means associated therewith. The additional heat exchanger 64 as well as the flow control valve 70 and the temperature-sensing means 72 may be of a conventional type such as that used at the surface production sites.

With either embodiment of FIGS. 2 or 3, it will be appreciated that the satellite 12 may serve a plurality of gas producing wells, one production line 26 associated with each well. in addition, a knockout section 38 and appropriate lines and control means associated therewith would be utilized for each subaqueous well served by the satellite 12.

It will be understood that the temperature of the gas may vary over a range of 25 to 35 F. upon entering the gas product line 52. In order to achieve the separation of the substantially waterfree gas, substantial cooling of the hot production fluid takes place. The following chart, which assumes a hot production fluid temperature of 140 to 150 F. is illustrative of the necessary cooling achieved at various points in the system:

production fluid line 26- 140" to 150 F.

gas section 32--- to F.

oil section 36-90 to 95 F.

knockout section 38- 120 to 130 F.

oil line 46- 120 to l 30 F.

gas line 50l20 to l30 F.

gas product line 52-25 to 35 F.

liquid product line 4490 to 95 F.

Certain modifications of the apparatus and method may be desirable to meet various conditions without departing from the scope of this invention. In particular, it may be desirable to provide a liquid product line and not an exclusively oil product line so that the three-phase knockout section 38 may be replaced by a two-phase knockout section which will separate gas from liquid. in such a case, the dual oil and water compartments 88 and 90 may be eliminated and replaced by a single compartment with a single drain line leading into the low-temperature separator. When a liquid product line is provided, other modifications such as the connection of the drain 162 into that product line become possible. Also, the various pneumatic and hydraulic control means may be replaced by equivalent means such as electrical control means.

It will therefore be readily apparent that the foregoing describes only two embodiments of the present invention and that many modifications may be made thereto without departing from the scope of the present invention as described by the following claims.

What I claim is: I

l. A subsea satellite for producing gas from subaqueous deposits with one or more submerged gas-producing wells having submerged wellhcads, said satellite comprising:

a watertight, pressure resistance shell;

a production line adapted to be connected to said one or more gas-producing wells, said production line extending into said shell;

a heat exchange means connected to said production line;

a liquid knockout means within said shell and having an inlet, a liquid outlet, and a gas outlet;

a first flowline connecting said heat exchange means with said inlet of said liquid knockout means;

a low-temperature separator within said shell and having an inlet, a liquid outlet, and a gas outlet, said heat exchange means comprising a section of said production line which passes through the liquid section of said low-temperature separator; and

a second flowline connecting said gas outlet of said liquid knockout means with said inlet of said separator 2. The subsea satellite of claim 1 including:

a choke means in said second flowline between said outlet of said liquid knockout means and said inlet of said separator.

3. The subsea satellite of claim 2 including:

means for injecting a hydrate depressant into said second flowline between said outlet of said liquid knockout means and said choke means.

4. The subsea satellite ofclaim 3 including:

a second heat exchange means located in said first flowline between said first-mentioned heat exchange means and said liquid knockout means.

5. The subsea satellite of claim 4 wherein:

said second heat exchange means provides for indirect heat exchange between fluids in said first flowline and fluids flowing from said gas outlet of said low-temperature separator. 

2. The subsea satellite of claim 1 including: a choke means in said second flowline between said outlet of said liquid knockout means and said inlet of said separator.
 3. The subsea satellite of claim 2 including: means for injecting a hydrate depressant into said second flowline between said outlet of said liquid knockout means and said choke means.
 4. The subsea satellite of claim 3 including: a second heat exchange means located in said first flowline between said first-mentioned heat exchange means and said liquid knockout means.
 5. The subsea satellite of claim 4 wherein: said second heat exchange means provides for indirect heat exchange between fluids in said first flowline and fluids flowing from said gas outlet of said low-temperature separator. 